Computing sight



Sept. 5, 1950 A E. H. L UDAEMAN'A n A 2,520,9434

COMPUTING SIGHT `Filed Aug. 5, 1947 4 shets-sheef 1 E. H. LUDEMANc`oMPUTING .SIGHT Slept. 5, 1950 4 Sheets-Sheet 2 Filed Aug. 5, 1947 lln/veniva Edwin Lud emu-n.

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Sept. 5, 1950 v E. H. UDEM`AN COMPUTING SIGHT 4 Sheets-Sheet v3 FiledAug. 5, 1947 Y SSN E dwn H- Ludemnn Mza.

SePt- 5, 1950 E. H. LUDEMAN 2,520,943

COMPUTING SIGHT Filed Aug. 5, 1947 4 Sheets-Sheet 4 Fig- 7 l E dWin H.Ludemun l Wma/MMM Patented Sept. 5, 1950 UNITED STATES FTENT OFFICE(Granted under the act of March `3, 178823, as amended pril 30, 1928;370 0. G. 7577) 27 Claims.

The invention described herein may be manufactured and used by or forthe Government for governmental purposes Without the payment of anyroyalty thereon.

This invention relates to lead-computing gun sights. It is well knownthat, to efeetively engage a moving target in combat, the gun must beaimed ahead of the target by an angle that is a factor of range, averagevelocity of the projectile, and speed of the target. In making suchcomputations, the assumption is necessarily made that the target willcontinue in rectilinear moven ment at constant Velocity during the timeof flight ci' the projectile. Under such conditions, the angle of leadis the angle subtended at the gun by a distance equal to the productofvelocity of target and time of flight of the projectile, such distancebeing laid on along the path of the target projected ahead of theposition of the target at the time the gun is fired.

It is therefore an object of my invention to provide a lead-computinggun sight that is entirely self-contained and that, except for .onemanual adjustment, operates automatically to compute and apply thenecessary lead-angle merely by the act of keeping a sight trained uponthe target.

A further object is to provide a sight of the type described whereinreticle lines are projected into the eld of view and are automaticallymoved and manipulated by the operation of the gun in tracking the targetso .that the gun has the proper lead when the target is properlypositioned or framed between the reticle lines.

Another object is to provide a leadecomputing sight of the typeaforesaiclwherein the apparent spacing of reticle range lines is variedin accordance with a function of the angular velocity of the target andrange.

A still further object is to provide a leadcomputing gun sight whereinan image of the reticie lines is projected into the'eld of viewincluding the target and the observable images varied along each of twomutually-normal coordinate axes in accordance with the .angular velocityof the target from the gun position.

Another object is to vary the relation ofthe scale of reticle lines inthe field of View of the telescope to correct for differences betweenthe actual and measured angular rates of the gun.

A further object is to provide .an angular raterneasuring mechanismwherein the settling time oi theinstrument, that is, the time requiredfor the instrument to reach 1a .steady state, varies in accordance witha function of the rate measured.

Yet another object is to provide an angular ratc-measuring mechanismwhich .is highly .accurate and sensitive to small changes iny angularrates and which, at the .sametinarnayzberene -2 dered insensitive tohigh rates, as when the gun is slet/,ed to piel; u p a new target.

Still another object is to provide a lead-computing gun sight that is,except for an initial setting for range, automatic in operation, that isoperable if desired, by one person, relatively simple in use,inexpensive to construct and capable of being used to a high degree ofaccuracy.

Another object is the provision of a method of determining the leadangle for a moving target by the mere act of moving a gun to maintain aline kof sight directed thereon.

@ther objects and advantages of my invention Will become :apparent asthe description proceeds.

AIn the drawings; 1

Fig. l isa velocity diagram taken in a plane determined by the gunposition and target `path and showing the principle upon which my com'-puter operates;

Fig. 2 is a vector diagram showing the lfactors determining the anglesubstended at the gun by the. assumed sphere lof diameter equal to thewing span of an aerial target;

Fig. 3 is a perspective View of the left side of a gun equipped with mylead computer and showing the manually-operated elevation and azimuthcontrols and their `extensions to the computer proper;

Fig. 4 -is .side elevation of .the computer With cover plate removed;

Fig. 5 is a sectional View to an enlarged scale, taken upon a plane asindicated by line '5-5, Fig. 6;

Fig. 6 is a View corresponding to a portion of Fig. 4, but on anenlarged scale and showing in section the casing mounting the variablespeed drive, sphere-driven castor and interconnected parts;

Fig. '7 is a View corresponding to a. portion of Fig. 4 and showing toan enlarged scale the means for projecting the reticle into the eld ofView of thesight;

Fig. 8 is a section taken upon a plane indicated by the line 8-8,'Fig.5-showing the perforated reticle-forming disc pivoted into a typicalposition;

Fig .9 is adetail View uponan enlarged: scale, of the knob for adjustingthe instrumentrto ob'- served or apparent target size.

Figs. 10 and 10a Show two typical views of a targetas seen whencorrectly framed between reticleglines, for large and small ranges,resp.ec. tively;

r.Figs- .1.1 land 12 show various suitable Ltypes of perforations in thereticleforming discnf, n

Fig. 13 is a Wiring diagram oi a circuit to prevent the production ofexcessive lead angles durassuma ing slewing or rapid angular movement ofthe gun, as when picking up a new target;

Fig. 14 is an elevational detail view of a modied form ofreticle-tilting mechanism;

Fig. 15 is a detail sectional view upon a plane indicated by the lineI5-I 5, Fig. 6;

Fig. 16 is a schematic view of a cosine corrector suitable for use inintroducing corrections for superelevation.

Referring to Fig. 1 wherein all points shown are supposed to lie in theslant plane determined by the gun and the target path, assumed to be astraight line, G indicates the position of a gun equipped with mycomputer, and which is to be red at a target pursuing a course indicatedby the line To-Tp. To indicates the present position of the target andTp the predicted or future position at which a shell from gun G willstrike the target. The distance To--Tp is, then, equal to the linearspeed S of the target, assumed to be constant, multiplied by the time ofiiight tp of the projectile from G to Tp. The angle A is the anglesubtended at the gun by the slant plane distance TQ-Tp or Stp.

From the figure, it is clear that, approximately,

EDctp Dp 1) Where A is the lead angle between the present and. futuregun-target lines, E is the angular velocity of the target in the slantplane as measured by the computer, tp is the time of flight of theprojectile, and Dp is the future or predicted range. Also. very closely,

Dp=vtp where o is the average velocity of the projectile to the point ofimpact Tp.

Substituting the value of Dp in (2) into (1),

sin A= Since A is always small, the difference between the angle and thesine thereof is negligible, whence,

For a given engagement, S is assumed to be constant during the travel ofthe target from To to C. Also for this run, TOC, as well as for anyother specic run, DM and v are constant. Hence the value of Equation 8is constant (k) and, for any tw particular Values of A such as A2 andA1,

HeIlCe all angular positions of its fore and aft axis relatively to thegun-target line so that the image of the target is in the correctposition relatively to the reticle lines or segments, in the mannersubsequently explained, From the gure D09=W or D0=W/0 (10) Equating thetwo values of Do of Equations 6 and 10,

and =(-Sm-2% (1l) For a given target run S, DM and W are constant Henceis constant C, and for any two particular values of 0, a1=C2 and 02:022

Hence bi 36 g-: and 02:01

Thus, by varying the linear size of the pattern of reticle range lineswithin a eld of view of the target, the correct lead angle between thegun and the line of sight to the target, may be introduced by framingthe target between two reticle range lines and varying the lineardimentions of the pattern in proportion to E".

The manner in which this is accomplished will be made clear from thesubsequent description of the operation.

Referring particularly to Fig. 3, I identifies a fixed base having aring gear 2 formed upon its periphery. An upper gun carriage includes adisc 3 pivoted at its center on base I and having a ange or skirt 4depending therefrom and serving to protect gear teeth 2. The carriagealso includes spaced standards 5 and 6, fixed to disc 3 and formed attheir upper ends with bearings, one of which is shown at 'I. Alignedtrunnions, not shown, extend from gun cradle 8 of gun 9 and arejournaled in bearings 'I to define a gun elevation or trunnion axis I0.

A gunners seat I I is adjustably mounted upon rotatable disc 3 by meansof a socket I2 and 90 arm I3 having a vertical portion tting in socketI2 and a horizontal portion slidably received by the sleeve I4 affixedto seat II. Set screws I5 threaded into the socket and sleeve, enableadjustment of seat II in a manner obvious from bracket I8. This shafthas its other end .attached to one end of the core of a flexible shaft23, whose other end extends to the computer and, as shown at Fig. 5, isthere xed to a shaft 34 journaled in a bracket 24 fixed to standard 5 bycap screws 25.

A stub shaft 26 is journaled in standard 5 and has an elevation handwheel 21 and a pinion 28 attached to its outer and inner ends,respectively. A second shaft 29 is journaled in standard 5 adjacent andparallel to shaft 29, and haslfixed thereto a pinion 30, in mesh withpinion 28, and a pinion 3l in mesh with'an elevation gear sector 32attached to cradle 8 concentric of trunnion axis i8. One end of the coreof a flexible shaft 33 is attached to the outer projecting end of shaft29. This shaft extends to the computer where its other end is attachedto a shaft 35 journaled in bracket 24. The hand wheel 21 is in positionconvenient to the right hand of the gunner in seat ll. The connectionsare such that each hand wheel rotates in a plane parallel to and in thesame sense as, the gun motion which it effects. Thus rotation of handwheel l1 clockwise looking down therein, rotates the gun clockwise intrain, while rotation of handwheel 21 clockwise, as seen in Fig. 3,elevates the gun. Thus the movements of the hand Wheels correspond tothe desired direction of movement of the gun, and facilitates smoothtracking, While reducing vertigo on the part of the gunner. The opticalparts of the instrument will be subsequently described but it should benoted at this point that the eyepiece or occular 35 is positionedconveniently to the eye of the gunner when in seat Il.

As best shown upon Fig. 5, a circular plate 36 is secured to bracket 24,concentric of trunnion axis I0. This plate has a central aperture inwhich a combined bracket and gear unit 31, is journaled for rotationabout axis I0. This bracket comprises a vertical arm 38v andN anintegral hub 39 fitting the aperture in plate 36, and having a gear 49attached to its end. Bracket 31 also has a horizontal arm 4l having abearing 43 on its outer end. A shaft 44 is journaled on a normallyvertical axis in this bearing and has a bevel gear 45 xed thereto. Atits top, shalt 44 carries a cup 156 on which a hollow sphere 41 restsand to which it is secured. The relations and dimensions are such thataxis I9 passes hrough the center of sphere 41. A 90 angle 42 is fixed tothe end of arm 4I. A shaft 43 is journaled at its ends in this angle andvertical arm 35, and has a pinion 49 in mesh with pinion 45. A gear 59is secured on shaft 48 and meshes with an idler gear 5l journaled on astud shaft 52 on arm 38. Idler 5l meshes with a gear 53 which is fixedto a shalt 54 journaled in a bearing aperture in hub 39 on axis l0. Abevel gear 53 forms one side of a differential 55 and is attached to theouter end of shaft 54. The other side 'of this differential comprises abevel pinion 55 and a gear 51 forming a composite element journaled onsli-ait The center of diierential 55 is formed el? two or more planetarygears 5,3 journaled on a shaft 59 fixed to the end of shaft 34, in amanner clear from -inspection 'of Fig. 5.

Shaft 35 is journaled at both ends in ybracket 24 and has a pair ofpinions 59 and El iixed thereto. An idler v62 is journaled on bracket 24and is in mesh both with gear 51 and .pinion '69. Pinion '6l is in meshwith gear 40.

"all-lie purpose of Ythe foregoing construction is gun.

6 to rotate bracket 31 equally andoppsil'ely to the movement of the gunas it changes elevation about axis It, to thereby maintain shaft 44vertical for all positions of the gun in elevation, and to rotate shaft44 equally and oppositely to movement of the gun in train to maintainall diameters of sphere 41 normal to the axis 'of shaft 44.; fixed indirection.

Considering the case where handwheel l1 only is being turned to therebytrain the gun. Shafts 23 and 34 are thus rotated proportionately todrive the planetary gears 58 of diierential 55. Since )ide 55 of thedifferential is motionless at this time, by reason of being xed throughgears 51', EL 536 to shaft Z" o which is not rotating, the drivecontinues through differential 55 by way of 'side 53 to shaft 54..Rotation of shaft'54lv rotates sphere 41 about the axis of shaft '44. byway of gears 53, 5i, 55.5, shaft 48, gears 49 and 45 and shaft 4?. Thedriving ratios are so selected' that, for any rotation oi 'gun tclockwise in azimuth, for example, sphere l1 will be given an equalrotation counterclcckwise. In this manner, sphere o1 .is maintainedfixed in azimuth for all posttions ci the gun in train.

Consider next the case where handwheel 21 amy is rotated to 'change theelevation angle of the gan. The resulting rotation of shafts 33 and 35.drives pinion 5l and thereby gear 49, to rotate bracket 3'? about axislli. The connections and ratios are such that for any given change inthe angie of gun elevation, bracket 31 is rotate@ equally and oppositelyto maintain. shaft 45.1 vertical However, in case gear 53 were heldstationary during change of elevation of the gun, dier 5i revolves orWalks around gear 53 as bracket 31 rotates about axis Il! relatively tothe The resulting rotation of gear 5I and sphere 41 would cause arotation in azimuth of sphere 41 which, unless compensated, would effeeterroneous operation of the computer. To compensate this rotation,operation of shaft 35 also effects a drive by way of gears 6i), '62 and51 to side of diierential 55. Since planetary Agears '53 are heldmotionless at this time, the drive continues through gears 58 and 63 toshaft 54 and thence, over the drive previously traced, to shaft t4 andsphere 41. The connections and gear ratiosV are such that gear 53 isrotatedV vin the .saine direction and to the same extent, as verticalarm 36. As a result, pure elevation of the gun causes equal and oppositerotation of bracket 31 about axis lll, while gear 5l remains motionlessrelatively to the bracket and no rotation of shaft ill and sphere 41 iseffected thereby. For clarity or description, the two angular movementsor" the 'gun have been separately explained. However, it will lbeunderstood that the mechanical action is not altered in any way when thegun is simultaneously trained and --elevated. The mechanism justdescribed maintains the two component motions separate and distinct sothat each is 'applied :to the sphere about an axis parall'el te thecorresponding -axis of `'gun movement. As a result sphere 41 ismaintained lrotationa'lly .space for all angular ymotion and for allangular positions yoi the gun. 1

The computer Ii's housed inra ycasing ifi which, as Vsl'iown by Fig. 3,is `fixed 'to cradle 8 by a lbracket t5. `A. removable lcover 3:6 closes`one side of the casing and is held in position by screws 1 engaging intapped apertures in lugs 38, Fig. 4.

The other side of casing B4 has an aperture 69,

Fig. lfsm'oothily fitting mate 36 and on which :it rotates. :as 'the-gun-fchange's elevation.

The tcp of casing 64 carries a frame I0 which. as best shown at Fig. 6',includes two raceways for antifriction bearings 1I and 12 dening an axisH2 concurrent with and normal to, axial I0, and also passing through thecenter of sphere 41. A frame or housing 13 is journaled in and by thesebearings. Frame also carries a plurality of slip rings 15 and 16 mountedon dielectric inserts carried by bars 11 located at spaced intervalsabout the frame. At its top casing 64 has an aperture closed by the maleportion 18 of a separable plug connector whose prongs 19 areelectrically connected with the respective slip rings 15 and 16. Housing13 has a dielectric plug 88 closing an aperture in its side wall. Brushconnectors 82 and 83 are mounted in this plug, each resiliently engaginga respective one of slip rings 15 and 16.

A constant speed motor 84 is mounted by flange 85 within an aperture inthe wall of housing 13 and has its leads 85 connected with respectiveconnect-ors 82 and 83. Motor 84 drives a disc 83 of a variable speeddrive 93 through reduction gearing including pinion 81 on the shaft ofmotor 84, gear 89, pinion 90 and gear 9|, the latter being xed to theshaft of disc 88. The reduction gearing, as Well as the disc, aremounted upon a support 92 xed to one end of housing 13.

Variable speed drive 93 is of conventional construction, and includesdriven roller 94 journaled cage for balls 98. This shaft also has a rack99 formed thereon and, at its inner end, carries a cam |80, whosepurpose and function will be subsequently described. The shaft 91 isguided for axial translation at the end adjacent cam |00, by rollers IOIjournaled on the housing wall. Such translation moves balls 98 radiallyof disc 88 so that roller 94 is driven at a speed proportional to theradial position of the balls.

The end of housing 13 remote from support 92 is open, to receive theadjacent portion of sphere 41. An arcuate slide |02 is mounted Withinthe open end of the housing concentric to the center of sphere l1 and isguided for angular movement about such center in a plane that passesthrough the center of the sphere for all rotational positions of housing13 about the axis of bearings 1I and 12. This plane coincides with theplane of the sheet of Fig. 6 for the positions of the parts there shown.The movement of slide |02 is guided by any suitable construction such asthat shown upon Fig. l5, where slide |02 is provided adjacent oppositeends with ribs Ia lying in a common diametral plane of sphere 41 andreceived in slots in the rim 13a. of housing 13.

While if desired, means may be provided to positively prevent separationof slide |02 from housing 13, it is contemplated that the slide may beheld in position by the action of a spring |03 and a roller or caster|05. Spring |03 is connected at one end to housing 13 and at its otherend to an eye |04 on slide |02. The position of the spring is such thatit exerts a force on slide |02, having one component holding the slideupon its seat, and a second component urging the slide into clockwiserotation as seen at Fig. 6. This latter component is sulcient to at alltimes hold a knob |06, secured to slide |02, in engagement with cam |00.In this manner, the axial position of shaft 91 and cam |00, determinesthe displacement of slide-|02 from its normal or central position.

Slide |02 has a slot |01 in its lower half Within which caster |05 isjournaled on a lever |08, pivoted to slide |02 atV |09. A spring ||0acts between an abutment III on slide |02, and lever |08, to urge caster|05 into contact with sphere 41. The caster is so mounted in slide |02that its point of contact with sphere 41 is at all times in the plane ofmovement of slide |02 about sphere 41 while its axis of rotation isperpendicular to that plane. Thus since housing 13 is free to turn aboutaxis II2, roller |05 acts to place itself in parallelism with the planeof rotation of casing 64 about sphere 41. Since the casing moves as aunit with the gun as the latter moves in tracking a moving target, thecaster thus acts to determine the apparent angle of approach ordeparture of the target, while the rate of rotation of the caster isdependent, with other factors, upon the speed of the target. Forexample, the position of the parts shown in Fig. 6, Icorresponds to acondition where the target is moving in a horizontal path directlytoward the gun position. The effect of the relative rotation of casing64 and sphere 41 can be readily visualized by imagining that the sphereis grasped and rotated in various planes about its center. Actuallyhowever, the sphere remains angularly xed while the casing 64 and partscarried thereby, rotate about its center aS the gun is moved to track atarget.

Caster |05 is mounted in arm |08, by a shaft having one end attached tothe core of a flexible shaft II3. The other end of this shaft II3 isconnected with a worm I I4 journaled in a portion of frame 96. This wormmeshes with a gear unitary with bevel pinion I I5 and forming one sideof a differential generally identied by numeral I I6. The -center ofdifferential IIB comprises a shaft II1 journaled in frame 96 and havingplanetary gears I I8 mounted on one end and a pinion I|9 on the otherend. A second side of diierential I i0 comprises a composite gear |20having one bevel pinion in mesh with planetary pinions I|8, and a secondbevel pinion in mesh with a pinion fixed to roller 94. The arrangementis such that side |20 of differential II6 is driven by motor 84 throughvariable speed device 93, in a direction opposite to that which caster|05 drives side I I5. Hence, when the two sides are rotating at equalspeeds, differential center I I8 is motionless and shaft 91 remains xedin position. This condition, for example, corresponds to a constantangular rate of tracking of the gun. However, when the rate changes therate of rotation of side II5 differs from the rate of rotation of side|20. As a result center II8, shaft II1 and pinion II9, are rotated toeffect axial translation of shaft 91 and shift balls 98 radially of disc88. This acts to vary the speed of roller 94 and diiferential side |20until the rates of the two sides are again equal. Thus, the axialposition of shaft 91 is proportional to, and measure of, the angularrate of gun movement in tracking the target. Incidentally, it should bementioned that housing 13 and all parts carried thereby, are balancedabout axis I I2 so that there is no pendulousness thereof and notendency of the same to rotate, apart from the control imparted bycaster |05. It will also be noted that axis II2 is maintained parallelto the bore axis of the gun.

From Figs. 4 and 6 it will be noted that housing 13 has a bevel gear I2Ixed to its end, and concentric of axis I I2. This gear has a centralaperture through which shaft 91 may pass with a.

smooth fit. Gear |2| meshes with and `drives a pinion |22 which is xedto the upper end of a shaft 23. This shaft is journaled in a frame |24attached to the adjacent wall of casing E4 and carries at its lower end,an elongated pinion |25 in mesh with a .ring gear |26 nxed to the upperend of one section of an optical unit identified generally by thenumeral |21.

The optical unit |2| includes three generally tubular axially, alignedsleeves. The upper sleeve |25 carries gear |25 and just below said gearis provided with a circumferential channel |3|. An opaque, perforatedreticle disc |32, Figs. '1 and 8, is provided with pivots |33 and |35,defining an axis coincidental with a diameter of the disc. These pivotsare journaled in aligned bearing apertures in sleeve |25 whereby thedisc is pivotallg,7 mounted in the sleeve. The pivot |34 extends beyondthe outer surface of the sleeve where it carries a lever arm |35. Theend of this lever is connected by a pivoted link |56, to intermediatesleeve |29.

Sleeves |28 and |29 are connected, by any suitable means, which permitsrelative axial translation only. Such means is shown, merely by way ofexample, with three guides |31, |38 and |39 extending upwardly from theperiphery thereof, each slidably received in a corresponding channel insleeve |28. Thus the two sleeves may have relative axial sliding but arecompelled to rotate as unit, and because or link connection |35, |33between the two sleeves, any relative axial motion effects aproportional pivotal movement of disc |512. The purpose and function ofthe perforations in the disc will be subsequently explained. Sleeve |25has a circumferential channel MI.

Sleeves |28 and 25 are thus mounted for independent movernent in thedirection of their common axis. This movement of sleeve |28 iscontrolled by a rod |52 guided for axial translation by a bearing |44 inframe |25 and a socket |45 formed in base |55. A projection |41,attached to shaft |22 has an arcuate end forming a rider fitting withinchannel 53| and identical with the |55 on the upper end or" the rod,into contact with a three-dimensional control cam iixed to a shaft |52.The purpose of this cam will be subsequently explained.

Likewise, rod |53 is guided for axial translation by a bearing |53provided in frame |24 and a socket |54 in base This rod has a projection|58 forming a rider at its end which rider engages in channel iai. Acoil spring |55 is located in socket |55 and acts to sup-port the Weightol rod |53 as well as sleeve |23, and to urge the anti'lrietion call |55at the ton of rod |53, upwardly into Contact with three-dimensional cam|51 xed upon shaft |52. It is contemplated that means may be providedfor adjusting the thrusts exerted by springs |45 and |55 such asadjustingI screws threaded through the base |45 and projecting intosockets |25 and i5 The lower sleeve i Se is adapted to have a snug fitwithin aligned apertures in base |55 and casing 5d and to be axiallyadjustable therein. Means for positively so adjusting the sleeve may beprovided if desired or found necessary. A circular bezel |58 is securedwithin sleeve |35 near its top and mounts a ground glass screen |59. Alens system, shown as a simple projecting lens |60, is secured over thelower 'end of sleeve |30 by a bezel ring |6| threaded thereon. A sourceof illumination .such as a lamp |62 and reflector |53 are mounted on thewall of casing 64 above and centrally of sleeve |28. This source acts tocause an image of the perforations to be Vprojected upon screen |55, toproduce an .image thereof which is projected by lens |35 `upon apartially silvered reilector |55 mounted by bracket |55 upon the Wall ofa sight'casing i 66. The reilector is positioned at 45 both to thecommon axis of sleeves I 28, |29 and |30, as Well as to the optical axisof eyepiece 35. f

The construction just described operates to project an image of theslots in disc |32, upon ground glass screen |59 and thence to reflector|64 so that the gunner, looking through eyepiece 35, may see an image ofthe reticle vsuperposed over the image of the target.

Shaft 52 is connected in alignment with a second shaft |58 by a swiveljoint |61. Shaft |58 is mounted in a bearingr |59 carried by the casingwall. Axial translation of shafts |68 and |52 as a unit, is effected bya lever |10 pivoted at 11|, Fig. 4, upon frame |24 and connected by apinand slot connection 1| to'shaft |68. Atits other end, lever |10 isconnected by a pin and slot connection |12 to a shaft |13. v'Shaft |13is mounted at one end in a bearing |15 on the wall of casing 54. Theother end of this shaft is connected by a swivel joint |15 to theadjacent end of'shaft 91. The two arms of the lever |15 areconveniently, but not necessarily, of equal length so that shaft |52 isaxially translated in the same amount, but in the opposite direction, asshaft 51 under the action of differential H6, pinion ||9 and rack'SS.This translation, it will beA remembered, is proportional to the rate ofrotation ofroller |05 over sphere 41 which, in turn, is proportional tothe angular rate of movement of the gun in the slant plane determined bythe gun position and target path. In short, shaft |52 and camsv |5| and|51 carried thereby, are translated axially in proportion to 2.

Shaft |52 has its end remote from joint'l61 splined as at |16, Fig. 9,to the sleeve'portion of an adjusting knob |11. This portion visjournaled in an aperture in casing 65 convenient to the gunner, as shownupon Fig. 3. Axial movement of the knob is prevented by acircumferential channel |18 and a screw |19 having its end engagedtherein. It is intended that knobV |11, shaft |52 and cams |5| and|51shall be rotated in accordance with the wing span ofthe target. Tofacilitate this adjustment, a scale |11a., grad# uated in wing spanmeasured in feet, for example, may ,be attached to casing 54, forcooperation with a pointer |1119 xed to rotate with knob |11. In thismanner, cams |5| andl 51 are axially translated in proportion to theangular velocity of movement of the gun in the target slant plane as thegun is moved to track a target; and-are rotated in proportion to thewing span of the tar-get.

In Fig. 14, I have shown a modification of the reticle disctilting'mechanism wherein the projecting end of pivot |35 has a pinionllsecured thereto, in mesh with a rack |8| pivoted at |83, to sleeve |25.The rack is held in engagement with the pinion by means of a leaf springV| 84. In thisv manner relative motion of the two sleeves effectstilting of disc |32 in exact lproportion t the amount of such motion.

Where a manually controlled source ofjpower -v is used to control thegun, rapid slewing of the gun, as when picking up a new target willgenerate excessive lead angles and lengthen thev time necessary for thecomputer to reach a new steady state and for successful engagement ofthe new target. To obviate this, I use the circuit shown in Fig. 13wherein are shown the leads 8E, supplying constant speed motor 84 undernormal operation, from ground at |84, lead |85, doublepole double-throwswitch |86, lead 14, governor switch |81, leads 8B, and current supply|88 to ground at |89.

Switch |88 is located in position for convenient operation by thegunner. Thus, Where a single handle-bar control is used, the switchwould be mounted directly thereon for ready operation. When so operated,connection between leads |85 and 14 is opened while connection is madebetween leads 8| and |90. The motor is now supplied over a circuit fromground at ISI, auxiliary source of potential |92, lead |88, switch |86,leads 8| and 86, to ground at |89. The additional potential from source|92 causes motor 84 to rotate at increased speed and, since the rapidangular movement of the gun cuases roller to rotate at a greater rate,excessive axial displacement of shaft 91 is avoided.

Operation The gunner has been trained to imagine the target surroundedand encompassed by a sphere having a diameter equal to its wing span W.This diameter is the controlling dimension used in framing the targetbetween the reticle lines. Tests were conducted to obtain an initialestimate of the errors that might be expected by reason of the variouspossible attitudes of a target craft with respect to the line of sight.It was found that the average error to be expected is 2.4%. thoseinherent in prior art gun-lead computing systems and may be furtherreduced by practice and experience in actual combat. Figs. l0 and 10ashow typical appearances of the target when correctly framedj the formerbeing for a large range and the latter for a small range.

As soon as a target has been selected and identied, knob |11 is turneduntil pointer |111) indicates upon scale I 11a the known wing span ofthe target. The gunner, while viewing the target through eyepiece 35manipulates his controls to move the gun at a rate and in a directionnecessary to continuously maintain the target framed between the imageof the reticle lines. Since sphere 41 is maintained rotationally fixed,this movement of the gun causes roller |85 to move over the surface ofthe sphere in the slant plane in which the gun moves. Since housing 13is pivoted in bearings 1| and 12, the caster action of roller |85, turnsthe housing until the plane of the roller lies in the aforesaid slantplane. This turning of housing 13, operates through gear |2|, pinion|22, shaft |23, pinion |25 and ring gear |25, to rotate sleeves |28 and|29 as a unit about their common axis, to thereby rotate disc |32. Thegear ratios and connections are such that the sleeves rotatesynchronously with housing 13 and the axis of symmetry of the image ofthe reticle lines is parallel to the plane of rotation of the roller |05and extends from the center of the field of view in the direction ofdisplacement of the roller relatively to the adjacent intersection ofaxis I2 with sphere 41. For example, in the position of the parts shownupon Fig. 6, the aforesaid axis would eX- This error is small incomparison tot;

12 tend vertically downward away from the center of the eld of view.

Because of the action of the variable speed drive 93, the differentialH5 and the connection with roller and shaft 91, the later is translatedaxially in proportion to the velocity of rotation of the roller. Thistranslation is imparted through joint |15, Fig. 4, shaft |13, lever |18,and shafts |88 and |52, to impart a proportional translation to cams |5|and |51. These two cams are essentially of the same shape, the onlydifference being that cam |51, connected to sleeve |29, in addition toimparting to sleeve |29 the same axial movement that is imparted tosleeve |28 by cam |5|, also imparts to sleeve |29 an additional axialmovement that is a function of the angular velocity of caster roller |85and the wing span of the target craft. The purpose of this feature willbe subsequently explained.

Translation of cams I5! and |51, then, effects axial movement of rods|42 and |43, respectively, and sleeves |28 and |29. This movement shiftsreticle disc |32 toward or from screen |59 and correspondingly variesthe size of the image cast thereon and upon partial reflector |64. Thecam |5| is shaped depending upon the constants oi' the instrument andthe average Velocity of the projectile for the most effective and usualrange of the gun, to translate the reticle proportional to the Squareroot of the angular velocity, e. g., proportional to E in accordancewith Equation 8, supra, so that any element thereof intersected by aradial plane through the axis of shaft |52, will translate sleeve |28 byan amount proportional to the square root of the angular speed of thecastor or roller |85. The actual distances by which the sleeve is movedfor any given translation of shaft |52, will, of course, depend upon theconstants of the instrument, the ammunition used, and the averageprojectile velocity for the usual or most elective range of the gun.Each said element corresponds, under the conditions noted, to a craft ofgiven wing span and is selected by rotation of knob |11 after the targetcraft has been identified as to type and size.

The lead angle thus computed is based upon the assumption that theaverage velocity of the projectile remains constant for all ranges. Thisof course is not strictly correct since the average velocity willdecrease with increase of range. Assuming that the path of the targetremains xed in direction during the period between initial observationand impact of the projectile, and that a perpendicular is dropped tothis path from the gun position and the intersection of the path and itsperpendicular is the mid-point of the path. That portion of the pathtraversed by the target up to mid-point is termed the incoming leg whilethat portion of the path traversed by the target after passing mid-pointis termed the outgoing leg.

On the incoming leg of the target path the angular speed of roller |05will be a little less than the actual angular velocity of the targetwhile on the outgoing leg, its angular speed will be a little greaterthan the actual value. At midpoint the two values are congruen Theslight errors thus introduced can be significantly reduced if theaverage velocity V0 of the projectile toI the present target position,To, is substituted for the velocity, o, to the point of impact Tp, usedin Equation 4. Thus, on the incoming leg, the value of Do/Vo is greaterthan the corresponding value or Do/c and the product of Do/Ve with 2 asmeasured by the instrument, will be very close to the required leadangle. Likewise, on the outgoing leg of the target/s path Dal/V is lessthan the corresponding value of DO/c and again the product of DO/Vo withZ as measured by the instrument, will afford substantially correctvalues of A.

If in addition, the error caused by assuming sin A to equal A, isreduced, accurate lead values are obtained.

The foregoing errors are substantially eliminated by the use of theadditional cam l? which, for increasing values ci E, for example,translates sleeve 29 a distance greater than the correspondingtranslation of sleeve i effected by cam ll, by an additional distance.'The cam is so proportioned that the corresponding pivotal movement ofdisc i312 is e function ol E and W.

Superelevation corrections may be introduced by pivotally mountingreiiector ld in sight casing 4&6 about a normaliy horiaontal axis lyingin the plane of the reflector. Since superelevation is a function ci thecosine of the angle oi' gun elevation, any well-known cosine correctormay be connected to be connected to be operated by elevation driveiii-32, inclusive. Such corrector may be directly connected to thepivotal mountn ing for the reector. Fig. l5 shows a suitable correctorfor this purpose where reflector lili-i is indicated in dotted lines andis pivoted in casing l upon a shaft SH3 having its axis in the piane ofthe reflector and to which a roller itil is attached. A second roller isjournaled a short distance from left. A frame iii@- has arms res ingupon rollers and isi whereby, in ccniunetion with auxiliary rollers i9?and ist the frame is guide for translation only. Frame iet has a slottherein, extending perpendicuiarly to the direction of translation ofthe frame. A nei;- ible steel band les extends about rollers it. and H35and may be secured to as indicated at This band has its ends connectedto frame ist at points such as 2li! and whereby translation of the frameeffects corresponding rotation of reflector ld. Preferably the arms ofthe frame rest upon the adjacent portions of the band. An eccentric itshas a smooth in the slot of traine ist and is journaled for rotationabout an anis offset from its center. in Fig. 1S the direction ci thisoffset is vertically downward so that, the position of the parte si'iowncorresponds to a 9G" angle or gun elevation with relector 351i at 45 tothe of gun bore. A tightener may be provided ior band tri# in the formof a roller 2te guided for movement transversely of and in Contact withthe band. Turning of screw 2:35 thus acts to tighten the band withoutcausing any rotation of roller i951. Elccentric 2% is connected by anysuitable drive means, not shown, for rotation by elevation shaft 3S orpinion (il. The driving ratio is .such that the eccentric is rotatedequally and oppostely to movement ci the gun in elevation and henceremains angulariy relatiifely to the vertical. Thus as the sight moveswith the gun in changing elevation, reflector i is pivoted in accordancewith the cosine of angle of gun elevation.

Corrections for changes in muzzle velocity of the projectile and in airdensity, may be effected by modifying the target size adjustment of knobil?. For example, scale Villa may itself be rotatable in accordance witha combined factor of muzzle velocity and air density. Knob lil may thenbe set relatively to the scale, in accordance with the known size of thetarget, as previously explained.

It will thus be noted that I have invented a lead-computing gun sightthat is relatively simple, entirely automatic in operation after settingfor target size, and simple and easy to operate. The proper lead angleis continuously introduced so long as the gun is properly tracking thetarget so that firing is limited only by the loading mechanism of thegun itself. Except for the motor 84, all parts are mechanical inoperation and there are no delicate and easily deranged telemetricdrives from a remote computer. The sight can be made relatively smalland compact and once attached and adjusted, remains constant inoperation throughout the life of the gun.

In the specification, the term elevational movement includes movement ofthe gun to clecrease its angle of elevation, as Well as movement toincrease its angle of elevation.Y l'

For simplicity of explanation and illustration; the gun has been shownas being directly manually actuated. This 'disclosure is illustrativeonly.V The' actual control used will depend'upon the type and size `cfgun'. It is clear'that, for guns of relatively large caliber, hydraulic`or electric power will be used under the controlof the gunner. Suchcontrol maybe 4elected by any of the Well-known joystik or handlebarcontrols where a single controlelement is used mounted for movement intwo ahgularl'yrelated planes. This element is connected to the powermeans such that movements inthe'tvvo planes effects motion of thegun incorrespond# ing planes. Suitable controls of this type are illustratedin the patents to Rolcik, 2,107,803, February 8, 1938, for AdjustingMechanism for Firearms and Adams et al., 2,350,662, June 6, 1944, forHydraulic System and Control. Any other of the control systems of thistype may be used so long as the motions of the gun in azimuth andelevation are transmitted to shafts 35i and 35 respectively.

The term axis of the reticle lines is the line corresponding to theradius of disc i232 about which the reticle range lines dened by slotsIM, are symmetrical. This axis, as shown upon Fig. 8, is perpendicularto the pivot axes determined by pivots |33 and |34.

The term framed as used in the claims means a, position of the gun andsight in which the imaginary sphere surrounding the target, and having adiameter equal to the Wing span of the target is tangent to both of thereticle range lines.

The caster angle of roller |05 is the angle deu Iined by axis H2 and theradius of sphere lil th'ugh the point of Contact of roller H35 therew1While I have disclosed the preferred form of the invention as now knownto me, it will be clear to those skilled in the art, to which thisspecication is addressed, that numerous substitutions of equivalents,and modications are possible without altering in any Way the basicprinciples upon which the instrument operates. It is 'therefore intendedthat the present disclosure shall be taken in an illustrative senseonly. It is my desire and intention to reserve all such changes as fallwithin the scope of the subjoined claims.

Having now fully disclosed my invention what I claim and desire tosecure by Letters Patent is:

i. In a computing gun sight Vadapt-ed to be carried by a gun for angularmovement'therewith in elevation and train, a bracket adapted to bejournaled on said gun for pivotal movement relatively to said gun abouta first axis coincident with the axis of gun elevation, a sphere pivotedon said bracket for rotation about a second axis coincident with adiameter of said sphere and normal to and concurrent with said firstaxis, a drive shaft journaled in said bracket coincidental with saidfirst axis, means carried by said bracket and connected with said shaftand sphere to rotate said sphere about said second axis in response toturning of said shaft, a differential having one side connected torotate said shaft, an azimuth shaft connected to drive a second side ofsaid differential, an elevation shaft, and means connecting saidelevation shaft to simultaneously rotate said bracket about said firstaxis and turn the third side of said differential.

2. In a lead-computing gun sight, a sphere adapted to be mounted upon agun for universal rotation with respect thereto, means connecting saidsphere with the gun to maintain the sphere angularly i'lxed for allpositions of train and elevation of said gun, a housing, means mountingsaid housing for angular movement as a unit with said gun and forrotation about a first axis coincident with a diameter of said sphereparallel to the bore axis of said gun, and roller means carried by saidhousing and in driven engagement with and rotated by said sphere wherebysaid housing is rotated about said rst axis in accordance with the planeof movement of said gun in tracking a target.

3. The combination with a gun elevatable upon a trainable support, asphere mounted upon said support for pivotal movement about a first axisparallel to the axis of elevation of said gun, and a second axis normalto said first axis, means responsive to change of elevation of said gunto rotate said sphere about said first axis equally and oppositely tosaid change to thereby maintain said second axis normally vertical,means responsive to training movement of said gun to rotate said sphereabout said second axis equally and oppositely to said movement, ahousing, means mounting said housing A.for elevation vand training withsaid gun and for rotation about a third axis parallel to the bore axisof the gun and forming a diameter of said sphere, a slide carried bysaid housing arcuately movable about the center of said sphere in aplane containing said third axis, a roller engaging said sphere andjournaled on said slide for rotation in said plane, said roller actingto turn said housing about said third axis in accordance with the planeof movement of said gun and third axis in tracking a target.

4. The combination specified in claim 3, a variable speed drive carriedby said housing, a motor connected to operate said drive, a differentialhaving one side connected with the output of said drive and a secondside connected to be driven by said roller, and means operating thespeed-varying element of said drive in response to operation of thethird side of said differential.

5. The combination specied in claim 3, a constant speed motor carried bysaid housing, a variable speed drive having an input operated by saidmotor and a speed-varying element translatable along said third axis, adifferential, a driving connection between a first side of saiddifferential and the output of said variable speed drive, meansoperating a second side of said dif- A16 ferential by and in response torotation of said roller, a driving connection between the third side ofsaid differential and said element, and means operable to move saidslide by and in response to translation of said element.

6. For use in a lead-computing gun sight, a housing adapted to movefwith the gun in elevation and train and rotatable about an axisparallel to the bore axis of a gun, a spherical surface adjacent saidhousing adapted to be angularly fixed, said axis being coincident with aradius of said surface, a slide mounted on said housing for rotationabout the center of said surface in a plane containing said axis, aroller journaled on said slide for rotation in said plane, meansyieldingly holding said roller in contact with said surface, .and meansoperable to angularly displace the point of contact of said roller andsphere from said axis proportional to the speed of rotation of saidroller over said surface.

7. In a lead-computing gun sight, a sphere, a roller, means mountingsaid roller in contact with said sphere for rotation thereby and forrevolution about a diameter of said sphere, and means responsive to therate of relative rotation of said roller and sphere about the center ofthe sphere to vary the angle between said diameter and the radius ofsaid sphere to the point of contact of said roller therewith.

8. In a lead-computer for guns, a sphere, a housing rotatable adjacentsaid sphere on a rst axis coincident with a diameter of said sphere, aroller, means carried by said housing mounting said roller in drivencontact with said sphere and for revolution about the center of saidsphere in a plane containing said rst axis and for rotation about asecond axis normal to said plane, and means responsive to the rate ofrotation of said roller about said second axis in response to rotationof said sphere about its center to revolve said roller relatively tosaid sphere in said plane and thereby to vary the angular relationbetween said rst axis and the radius of said sphere to the point ofcontact of said roller.

9. In a lead-computing gun sighting device, a sphere, a housingrotatable about a first axis coincident with a diameter of said sphere,a Variable speed power drive carried by said housing, a slraft axiallytranslatable in said housing along said first axis, means varying thedriving ratio of said variable speed drive by and in response totranslation of said shaft, first means connected to rotate with saidhousing about said rst axis and slidable in an arcuate path about thecenter of said sphere in a plane containing said first axis, a rollercarried by said means in driven engagement with said sphere androtatable about a second axis nonmal to said plane, a differentialcarried by said housing, and having first and second sides drivenrespectively by said roller and the output of said variable speed drive,means connecting a third side of said differential to axially translatesaid Shaft, and means to slide said first means by and in response totranslation of said shaft to vary the displacement of said roller fromsaid first axis in accordance with a function of the speed of rotationof said roller about said second axis.

10, The device recited in claim 9, said last named means including a camsecured to said shaft and engaging a portion of said rst means todisplace the same, said cam being formed to displace said roller inaccordance with the square ltion of said roller about said second axis.'l"11. "In a computing gun sight, a casing adapted to be montedforlmovmentvvith 'a""gtin'"in l'ei: Vation and train, means/"carridby Saidcasing din'g a iiriof'signt`para111 td tiratore 41ai s'adgun andincludiig'a feld f viewsurr'ounding'saiii une; a disc' beariiig'a'pairor reticia'rari'ge lines thereon symmetrical ab'i't ah'axis, nfeansprojecting an image of said1iri'es"'intof 'said eld of view, meansVresponsive to the nive'r'entf saidl gun in trackig'a t'argetto maintainthe axis if said reticie lines parallela@'tiiaapparerit path of movementof' the target, an'cn'feaiis" r'ei sponsiveto the rate' of A'aiflgilla'i"Iilo'veliient'tif said gun' and sight to bodily moi/'esairl'disc "relatively to said'casing to 'vary tlie apparent siZe"oi"th-e 'page 'of said reiici unas in arcor' with a function of saidrate.' :12."In a computing-sight for a gun, a frame adapted to movesynchronously with 'said gun in train andelevation i`n`tracliii`g amoving target, rst means responsive to` moveme'nt 'o'f saidgun intracking a target to determine the directiorf the path of saidYmovement,"secondi'means r'espcnsive to said movement to `deterniinetlfieangular rate thereof, a sighting'device'determining'a line of sightparallel' to rthe bor'e'of said gu'nan'd d ening'a field ofview'surrdundihgsaid nire, means defining apair'of parabolic'reticlerange lines symmetrical about an 'ax'isgv means 'project'- ing animageof said'lihesintsaidldiview with said axis concurrent with saidline of signi, means responsive to said iirst means to rotate'said axisaboutsaid line to Inair'tain'saidaxilal parallel to the plane ofmovement of the gun Lasit i's'm'oved te cause said line of sightto trackther target', and means responsive to said second means t Ava'ryth'eseparation of the images of saidlinesas' seenin root of the rate of rotsaid iield of vievv in accordance with the rate of angular movement of'said gun.

13. A computing gun sight for a gun elevatable upon a trainable platfrmc0m`p`r`isig`a casing adapted to be connected With 'sai'clg'un' formove'- ment as a unit therewith, istineans carried' 'by said casing todetermine a 'line fs'i'glitsub'stan'- tially parallel with said gun andincludng'a'iie'ld of View about said line, second means? in said'oasingdefining a pairof spaced reticle range lines symmetrical about an axis,means projecting an image of said ylines into said field of View withsaid axis concurrent'vvithsaidline, means re snensiye .to .angularmovement o f Vsaid gun in tracling a target maintaining said -axisparallel with the apparent path ofsaid target, a nd means responsive' tethe rate of said' anulanmovement to move said second means to 'vary thelinear di'- mensions of the image of saidline's.

14. In a lead-computing" gun" sight, first and second elements connectedfor rotation asa 'unit about a first axis and mounted vfor independenttranslation along said axis, a reticle disc".ni'voted on said firstelement on a second'axis normaltb said is't'axis and lyingin the plaideof "saiddis'c, means pivoting said disc about "said seonaxis hy and inresponse to relative'axial.translation of normai 'ibisaiii""nrstraxisand' lying firrftireipiaria r'sad disci' near'is torprojeet arimage-brama ond axis.

"17".For use in a lead-computing gun sight, a y

sighting meansfadapted tow 4lbe rnaimaine-ai"par-l allel t the'borelaxis of agun and t'include` a field view"about klsaid axis","rst'and secnd sleeves' connectedfor "c'on'joir't rotation aboutffa discin response to relative axial translation' of Speeder said;gun'rriovereiit and akriownninin;

sion of the target?"v '18."".A"'le ad'cmputing gun-sight comprising a sig'htfmzeans'deninga 'pair Vof parabolic reticl'e range liliessyirn'netr'ical ahou'taiiaxi's; meansto project an imagilof s aid linesintd thefe'ld l'of the 'fildof 'view r:of said "sighting'rneans, saidlinesleing` symmetrical "aboiian"i axis radial-'af said iield* ofiView," means' responsive -to iangular n'riovementv of' said 'sightingmeansimmantainig amoving target 'framed btweensaidilines;,to rotate'said-axis into"tparallelismwith the apparentpath of said'targetyandmeansto .vary-tl1e scalefof "said lines "as lviewedin 'saidsighting means, iniaccordance with the Wingspan ni' said target;andthd'square root of the rate Q angular"movement"d'said sighting'.meaIlS, '20.l` In a Sleadi-computing'Y gun sight', sightingmeansmea'ns operable .to projecttheimage gf twi).V reticle range linesinto Athe ield of view of saidsighting vni'eans, said;` imagelinesbeingsym-V 'the` nietrica'l aboutan axis extendingradially 9 M center ofsaidfield of. View, means responsivelto angular movement of said sightingmeans amado-r maintaining a moving aircraft framed between said lines torotate said axis into the plane of said movement, and means adjustablein accordance with the wing span of said aircraft and automaticallyresponsive to the rate of said angular movement, to vary the scale ofsaid image lines in said field of View.

21. In a lead-computing gun sight adapted to be mounted for movement asa unit in train and elevation with a gun, a sight including a partiallysilvered reflector interposed at an angle across the eld of View of saidsight and pivoted on an axis in the plane of said reector transverselyof said sight, means projecting an image of a pair of reticle rangelines upon said reflector, said image lines being symmetrical about anaxis radial of said field of View, and means responsive to the angle ofgun elevation to pivot said reflector in accordance with the cosine ofsaid angle to correct said sight from superelevation.

22. In a lead-computing gun sight, a casing adapted to be mounted formovement as a unit with a gun in train and elevation, a sphericalsurface, means rotating said surface about its center in response toangular movement of said gun, a housing in said casing rotatable on aiirst axis parallel to the bore axis of said gun and forming a radius ofsaid surface, a slide guided for movement on said housing in an arcuatepath about the center of said surface and in a plane containing saidfirst axis, a caster engaging said surface and rotatable on said slideon an axis normal to said plane, a shaft in said housing extending alongsaid iirst axis, means responsive to rotation of said caster over saidsurface to p,-

axially translate said shaft proportional to the rate of casterrotation, a sighting means movable with said casing in parallelism withsaid rst axis, an optical unit in said casing to project the image ofspaced, symmetrical reticle range lines into the field of view of saidsighting means, said unit comprising a pair of elements relativelytranslatable along a common second axis and rotatable as a unit aboutsaid second axis, a reticle disc pivoted on one said element andconnected with the other said element for pivoting in response torelative translation of said elements, means rotating said elementsabout said second axis in response to rotation of said housing by saidcaster about said iirst axis, and means dierentially translating saidelements to thereby pivot said disc in response to translation of saidshaft.

23. A computing gun sight as specified in claim 22, said last-namedmeans comprising a second shaft, iirst and second three-dimensional camsthereon, means operable by said cams in one dimension to differentiallytranslate said elements, respectively, and manually operable means foradjusting said cams in a second dimension in accordance with a knowndimension of a target.

24. That method of aiming a gun at a moving target comprising,establishing a line of sight parallel to said gun and including vasurrounding field of View, providing a pair of reticle range lines insaid field of View, symmetrical about an axis radial of said line ofsight, rotating said axis about said line of sight to maintain the, sameparallel to the apparent path of said target as said gun and sight areangularly moved to maintain said target framed between said reticlelines, and varying the spacing of said lines in accordance with afunction of the rate of said angular movement.

25. That method of aiming a gun at a moving 20 target, comprising,establishing a line of sight parallel to said gun and surrounded by afield of view, providing a pair of spaced reticle range lines in saidfield, symmetrical about an axis extending radially of said line ofsight, angularly moving said gun and line of sight as a unit to maintainthe target framed between said reticle lines, simultaneously rotatingsaid axis to maintain the same parallel to the apparent path of saidtarget, and varying the spacing of said reticle range lines inaccordance with the square root of the rate of angular movement of saidgun, while maintaining said target framed therebetween.

26. In a lead-computing gun sight, a casing carried by a gun to movetherewith in train and elevation, a sphere in said casing, meansmaintaining said sphere xed against rotation for all angular positionsof said gun, a frame journaled in said casing for rotation on a rst axisparallel to said gun and passing through the center of said sphere, acaster engaging said sphere and mounted on said frame for angularmovement about the center df said sphere in a plane containing said rstaxis and for rotation in said plane, a motor carried by said frame, avariable speed drive driven by said motor, a diierential carried by saidframe and having one side driven by the output of said variable speeddrive, a second side driven by rotation of said caster and a third sideconnected to Vary the speed of said variable speed drive, and meansdriven by said third side to alter the caster angle of said caster aboutsaid sphere.

27. In a lead computer for a gun, a fixed sphere, a support, meansmounting said support for angular movement about the center of saidsphere in synchronism with the gun and for rotation about a iirst axiscoincident with a diameter of said sphere, a roller, means mounting saidroller on said support for driven contact with said sphere forrevolution about said sphere in a plane containing said rst axis, andfor rotation about a second axis normal to said plane, and meansresponsive to rotation of said roller for revolving the same about saidsphere to vary the angular relation between said first axis and theradius of said sphere to the point of contact of said roller therewith.

EDWIN II. LUDEMAN.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,880,174 Dugan Sept. 27, 19321,913,793 Clementi et al June 13, 1933 1,963,457 Avery June 19, 19342,069,417 Murtagh et al. Feb. 2, 1937 2,139,636 House Dec. 6, 19382,339,508 Newell Jan. 18, 1944 2,372,613 Svoboda Mar. 27, 1945 2,383,952Bates Sept. 4, 1945 2,396,701 I-Iolschuh et al Mar. 19, i946 2,405,028Ford July 30, 1946 2,407,665 I-Iolschuh et al Sept. 17, 1946 2,426,744Polntius et al. Sept. 2, 1947 2,428,870 Essex Oct. 14, 1947 2,430,108Crooke et al. Nov. 4, 1947 FOREIGN PATENTS Number Country Date 777,913France Dec. 15, 1934 852,200 France Oct. 23, 1939

